In a fuel tank, fuel vapours form in the volume of the tank which is not filled up by liquid fuel. These fuel vapours represent potential emissions, which pursuant to various legal regulations must not be released into the environment, and thus must not leave the closed fuel system in an uncontrolled manner. The formation of the fuel vapours is influenced by temperature fluctuations, which are brought about both by fluctuating ambient temperatures and by heated fuel which is fed back by the fuel supply system. As the temperature increases, the formation of fuel vapours increases, partly because the saturated vapour pressure of the fuel vapour increases, and leads to a pressure increase in the fuel tank above the ambient pressure. Since fuel tanks become more complex and thus more expensive with increasing pressure resistance, the pressure is to be limited by ventilating the fuel tank to an acceptable level. Conventional tank ventilations pass the fuel vapour/air mixture through a container, in which the volatile fuel components are applied to an adsorbent, generally activated carbon, and emit purified air to the environment. Aside from the pressure increase in the tank as a result of the rise in the temperature of the fuel, a large amount of fuel vapour/air mixture is displaced by inflowing fuel when the tank is refilled with fuel. This mixture is either passed through the same or a further activated carbon container (ACC) or sucked out through a suction system in the nozzle of the tank system. The activated carbon containers have a limited intake capacity, which depends on the adsorbency and the size of the container. Beyond this intake capacity, fuel vapours are passed through the ACC without being adsorbed, and are thus released into the environment. To prevent this, ACCs of this type have to be regenerated regularly, or independently of the used capacity thereof.
Published application DE 101 38 280 A1 discloses a device for controlling fuel vapour purging in a vehicle, a valve arrangement merely passing the fuel vapours in a first direction from the fuel tank to a device for buffering the fuel vapours, and merely passing the fuel vapours in a second direction counter to the first direction into a combustion engine from the device for buffering fuel vapours.
Patent specification EP 0 444 517 B1 discloses a self-diagnosis device in a system which prevents the spread of fuel evaporation gas, comprising a canister, connected to a fuel container, for adsorbing the fuel vapour, the canister being connected to the suction duct of an internal combustion engine via an outlet duct. An opening and closing means is arranged in the outlet duct. The device further comprises an air/fuel ratio sensing means for detecting an air/fuel mixture passed to the internal combustion engine and an abnormality assessment means. This controls the opening and closing means and detects changes in the air/fuel mixture when the outlet duct is open and closed. On this basis, an assessment is made as to whether a particular abnormality is present. The self-diagnosis device further comprises an evaporation gas production state detection means for detecting the existence of fuel vapour and a three-way valve having a first terminal connected to the fuel container, a second terminal connected to the canister, and a third terminal connected to the suction duct. In a first position of the three-way valve, the fuel container is connected to the canister, and in a second position, the fuel container is connected to the suction duct. The abnormality assessment means switches the three-way valve from the first to the second position, detects a change in the state of the fuel evaporation gas, and assesses whether the evaporation gas production state detection means is abnormal.
Published application DE 10 2004 021 387 A1 discloses an internal combustion engine comprising a suction line, a mechanical supercharger, and a throttle body close to the motor, a further throttle body being arranged upstream from a supercharger in the suction line and at least one underpressure line branching off in a region between the further throttle body and the supercharger.
Patent specification DE 102 01 889 D4 discloses a control/regulation system for automatically stopping and starting an engine of a vehicle, comprising a fuel tank, a canister for absorbing fuel vapour generated in the fuel tank and purging the absorbed fuel vapour into an air suction system of the engine, a pressure control/regulation portion for controlling/regulating the internal pressure of the fuel tank, an engine stop/start determination portion, the internal pressure being kept at a predetermined level lower than atmospheric pressure, and the engine stop/start determination portion preventing the engine from stopping when the internal pressure is higher than the predetermined level.
A drawback of the fuel vapour purging devices used in the art is that the fuel tank is purged constantly via the activated carbon container, meaning that said container has to be replenished regularly, worsening the durability of the ACC and increasing the chance of a breakout, in other words emission of fuel vapour to the environment.